The present invention relates generally a cable laying machine including a plow with readily replaceable wear parts. More particularly, the present invention relates to readily replaceable plow points and shank guards adapted for use with cable laying assemblies. The replaceable wear parts are particularly well suited for attachment to plows used in conjunction with a vibratory cable laying machine.
In order to lay a cable in the ground, a trench of suitable size and depth to receive the cable must be dug. The cable is then laid in the trench, and the trench refilled and packed down. For large scale cable laying operations, a tractor having a moveable arm somewhat similar to a backhoe arm, is fitted with a plow shank, as shown in FIG. 1. Normally, a cable feed tube is attached to or incorporated into the back of the plow shank and a spool of cable located somewhere on the tractor feeds cable to the cable feed tube. The plow generally includes a shank having a cutting point that is wider than the cable being laid. Thus, as a tractor moves forward, thereby dragging the plow through the ground, the plow point rips a trench through the ground. The cable is simultaneously dispensed from the cable spool, through the cable feed tube, and into the newly formed trench.
While some so-called static plows are merely dragged through the ground as the tractor moves forward, a much more efficient digging and ripping operation is provided when a vibratory action similar to that of a jackhammer is imparted to the plow. This vibratory action is particularly helpful when cutting a trench through hard ground and/or rocky soil. Also, the vibratory plows can be effectively powered by engines that are smaller than (and with less energy consumption than) engines required for static plows.
To extend the life of the plow, conventional plows have incorporated such features as a replaceable tip or point covering a nose located on the extreme bottom and front of the shank and/or replaceable shank guards disposed immediately above the replaceable point on the lead or front edge of the shank to protect the surfaces of the plow most susceptible to wear.
The nose is typically welded onto the leading bottom edge of the plow shank and is normally wider than the plow shank. Thus, the plow point disposed over the nose normally sustains the greatest amount of wear and therefore is preferably replaceable. Both the nose and its associated plow point are normally tapered, with the plow point being hollowed so as to snugly cover the nose. The conventional method for attaching the point to the tapered nose is to insert a pin crosswise through one wall of the point, through the nose, and out the opposite wall of the point, as depicted in FIG. 2. The replaceable points must be manufactured to provide some leeway and tolerance for alignment of the holes through which the crosspin extends, thereby necessarily resulting in a loose fit and wobble between the point and the nose. Such loose fit causes forces applied to the point to be transferred through the crosspin and to the nose. The crosspins consequently are subject to immense forces tending to bend or displace the crosspins and to further loosen and disattach the point. While such arrangements are adequate for static plows which are merely dragged through the ground, they are totally unsuitable for vibratory plows.
Shank guards have also been traditionally attached to the leading edge of a bar shank to act as a replaceable wear surface for the leading edge of the shank itself. However, since conventional shank guards are attached to the plow shank by a crosspin in the same manner as the plow points previously described, they too are ineffective when used in conjunction with vibratory plows.
Thus, prior to the present invention, vibratory cable laying plows utilized a plow point and a shank guard that had to be welded to the shank itself or utilized replaceable points and guards subject to rapid deterioration and detachment. When a point welded to a plow wears out, either the entire plow shank must be replaced or the worn point must be cut off and a new one welded into place. Obviously, such practices are wasteful and expensive and cause an undue shutdown of cable laying operations. Similarly, replaceable plow points and shank guards attached to the plow by ineffective means tend to loosen and deteriorate rapidly, thereby resulting in the same drawbacks.
Consequently, there is a need for a plow with readily replaceable parts in the form of plow points and shank guards capable of functioning effectively with a relatively long life in the environment of a vibratory cable laying plow.